1. Field of the Invention
The present invention relates generally to spindle motors for use in a disk drives, and more particularly to a spindle motor including a magnetic element for pre-loading a ball bearing set.
2. Description of the Prior Art
The typical hard disk drive includes a disk drive base, and a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to the disk drive base. The head disk assembly includes at least one magnetic disk, a spindle motor for rotating the disk, and a head stack assembly (HSA) that includes at least one transducer head, typically several, for reading and writing data from and to the disk. The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk.
The spindle motor typically includes a spindle motor base, a central shaft, a rotatable hub, a stator, a magnet attached to the hub, and vertically spaced upper and lower ball bearing sets mounted upon the central shaft which facilitate rotational attachment of the hub to the spindle motor base. Each ball bearing set includes inner and outer ball bearing races which encase a plurality of ball bearings. The inner ball bearing races engage the central shaft and the outer ball bearing races engage the hub. This configuration allows for rotational movement of the outer ball bearing races relative to the inner ball bearing races for rotation of the hub. The hub further includes an outer flange which is used to support one or more of the disks. The upper and lower ball bearing sets are pre-loaded in compression to maintain the hub and the disks supported on the hub in an orthogonal configuration with respect to the central shaft. The stator includes a series of coils and is concentrically positioned about the central shaft, adjacent the hub. With this general configuration, the various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet otherwise associated with the hub, thereby imparting a rotational motion onto the hub. Rotation of the hub results in the rotation of the attached disks.
A topic of concern is the desire to reduce the overall disk drive size. Such disk drives may have a variety of applications such as in hand held or portable electronic devices. The exterior size and shape of the disk drive is often referred to as a “form factor”. Reduction of such disk drive form factor has proven challenging. This is because the mere reduction of the size of the various disk drive components may result in such components being unable to conform to required specifications and standard form factors for such components, and may result in installation or assembly difficulties. As such reduced sized disk drives may have applications in hand held or mobile electronic device, the specifications may be even tighter as compared to personal computer applications. For example, those specifications related to susceptibility to damage resulting from shock.
One particular area of focus is the reduction of the height of the spindle motor. In a typical configuration, the spindle motor height may be a function of the upper and lower ball bearing set arrangement. The mere reduction of the sizing of the upper and lower ball bearing sets impacts the susceptibility to damage resulting from shock, potential use of non-standard form factor bearing sets, and difficulties in conforming to allotted space requirements for such bearings. Accordingly, there is a need in the art for an improved spindle motor ball bearing configuration in comparison to the prior art.